Thin film metrology

ABSTRACT

A method of evaluating a thickness of a film on a substrate includes detecting atomic force responses of the film to exposure of electromagnetic radiation in the infrared portion of the electromagnetic spectrum. The use of atomic force microscopy to evaluate thicknesses of thin films avoids underlayer noise commonly encountered when optical metrology techniques are utilized to evaluate film thicknesses. Such underlayer noise adversely impacts the accuracy of the thickness evaluation.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application claims priority to U.S. application Ser. No.17/194,934, filed on Mar. 8, 2021, which claims the benefit from U.S.Provisional Patent Application No. 63/027,066, filed on May 19, 2020,titled THIN FILM THICKNESS METROLOGY. The applications are incorporatedherein by reference in its entirety.

BACKGROUND

There has been a continuous demand for increasing computing power inelectronic devices including smart phones, tablets, desktop computers,laptop computers and many other kinds of electronic devices. Integratedcircuits provide the computing power for these electronic devices. Oneway to increase computing power in integrated circuits is to increasethe number of transistors and other integrated circuit features that canbe included for a given area of semiconductor substrate. The number oftransistors that can be included for a given area of semiconductorsubstrate can be increased by reducing the size of the transistors.Reducing the size of the transistors may involve altering thethicknesses of layers of material as well the geometry of featurescreated on the semiconductor substrate. In the design process ofreducing the size of transistors, it is important to evaluate thethickness of the layers of material used to form the transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of substrate onto which two thin filmshave been deposited and which is subjected to an optical metrologyprocess.

FIG. 2 is a schematic diagram of an infrared atomic force microscopysystem useful in accordance with some embodiments of the presentdisclosure.

FIG. 3A is a cross-sectional view of substrate onto which two thin filmshave been deposited and which is being subjected to an infrared atomicforce microscopy process in accordance with an embodiment of the presentdisclosure.

FIG. 3B is a plot of atomic force microscopy tip force as a function ofscanned infrared radiation wavelength to which the films of FIG. 3A areexposed in accordance with an embodiment of the present disclosure.

FIG. 4A is a cross-sectional view of substrate onto which two thin filmshave been deposited and which is being subjected to an infrared atomicforce microscopy process in accordance with an embodiment of the presentdisclosure.

FIG. 4B is a plot of atomic force microscopy tip force as a function ofscanned infrared radiation wavelength to which the films of FIG. 4A areexposed in accordance with an embodiment of the present disclosure.

FIG. 5 is an example of a lookup table of force responses generated byinfrared atomic force microscopy correlated with measured filmthicknesses in accordance with an embodiment of the present disclosure.

FIG. 6 is an example of a lookup table of force responses at twodifferent wavelengths generated by infrared atomic force microscopycorrelated with measured film thicknesses in accordance with anembodiment of the present disclosure.

FIG. 7 is a flowchart of a method of evaluating a thickness of a film ona substrate in accordance with an embodiment of the present disclosure.

FIG. 8 is a flowchart of a method of evaluating a thickness of a film ona substrate in accordance with an embodiment of the present disclosure.

FIG. 9 is a flowchart of a method of evaluating a thickness of a film ona substrate in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

One embodiment described herein is a method for evaluating thickness ofa film on a substrate. Examples of a film include conductive andnonconductive layers of material on a substrate, e.g., a semiconductorsubstrate such as a silicon wafer. In an embodiment, a force response ofone or more films of material on the substrate to exposure to one ormore wavelengths of nonvisible electromagnetic radiation is detected.The detected force response is used to determine a thickness of thefilm. In some embodiments, the detected force response is a result ofexposing more than one film layer, e.g., a plurality of film layers onthe substrate, to the nonvisible electromagnetic radiation. Inaccordance with some disclosed embodiments, the thickness of the film isevaluated, e.g., determined, by identifying a film thickness in a lookuptable of force responses and film thicknesses for a material from whichthe film is formed. In other embodiments, a capacitance response of oneor more films of material on the substrate is detected. The detectedcapacitance response is used to evaluate, e.g., determine, a thicknessof the film. In accordance with some disclosed embodiments, thethickness of the film is evaluated, e.g., determined, by identifying afilm thickness in a lookup table of capacitance responses and filmthicknesses for a material from which the film is formed.

Optimization of processes used to manufacture semiconductor devices,e.g., transistors, involves evaluation of changes in materials,thicknesses, widths, pitches, geometry and other characteristics offeatures formed on a semiconductor substrate. Semiconductor substratesoften include tens, if not hundreds, of layers of thin films.Thicknesses of layers of thin films on semiconductor substrates havebeen evaluated using optical metrology techniques. Referring to FIG. 1,an example of an optical metrology technique is illustrated. In FIG. 1,the article being subjected to an optical metrology technique includes awafer substrate 10 upon which a first film 12 has been formed on thewafer substrate 10 and a second film 14 has been formed on the firstfilm 12. Optical metrology directs visible light 18 onto an uppersurface 16 of the second film layer 14. A portion of the incidentvisible light penetrates through second film layer 14 and reaches firstfilm layer 12. Some of the incident visible light that reaches firstfilm layer 12 may reach the interface between the first film layer 12and wafer substrate 10. A portion 20 of the incident visible light 18 isreflected by second film 14. Portions 22 and 24 of the incident visiblelight 18 is reflected by the first film 12 and results in undesirable“underlayer” noise with respect to the signal represented by portion 20of reflected visible light. Such underlayer noise reduces the usefulnessof the signal, represented by portion 20 of visible light, for purposesof evaluating the thickness of second film 14, e.g., thickness of thesurface layer film 14.

Referring to FIG. 2, in accordance with some embodiments of the presentdisclosure, infrared atomic force microscopy (IR-AFM) is utilized toevaluate thicknesses of thin film layers on a substrate. The signalsgenerated by the infrared atomic force microscopy are less susceptibleto the generation of underlayer noise associated with optical metrologytechniques. In FIG. 2, a block diagram of an infrared atomic forcemicroscopy system 100 useful in accordance with an embodiment of thepresent disclosure is shown. The IR-AFM system 100 includes a computer102, which controls various components of the IR-AFM system andprocesses the resulting infrared atomic force (IR-F) signals. The IR-AFMsystem 100 further includes a cantilever 104 with a probe tip 106, apiezoelectric transducer or a dither piezo 108, a phase locked loop(PLL) cantilever driver 110 and a deflection sensor 112. In someembodiments, the dither piezo 108 creates vibrations on the cantilever104 to make the probe tip 106 oscillate, e.g., at one of the resonantmodes of the cantilever, as the probe tip is moved over a sample ofinterest 114 to image the sample. The dither piezo 108 is driven by thePLL cantilever driver 110, which provides a driving signal to the ditherpiezo. The PLL cantilever driver 110 is connected to the deflectionsensor 112, which optically senses the vibrations (e.g., frequencyand/or amplitude) or displacement of the cantilever 104 using a lightsource, e.g., a laser diode, and a photodetector, e.g., a photodiodedetector (not shown). As an alternative to deflection sensor 112, IR-AFMsystem 100 can include a sensor capable of detecting changes in distancebetween the probe tip 106 and/or cantilever 104 from upper surface 16 ofsample 114. In some embodiments, the PLL cantilever driver 110 generatesa driving signal whose frequency tracks changes in the resonancefrequency of the cantilever 104 due to force gradients acting betweenthe probe tip 106 and the sample 114, which may include IR-F. Thisfrequency tracking is accomplished by a phase locked loop in the PLLcantilever driver 110 that measures the phase of the cantilevervibration relative to its driving signal, and adjusts the frequency ofthe driving signal to maintain a fixed phase relationship between thedriving signal and the cantilever vibration. The cantilever 104 with theprobe tip 106, the dither piezo 108, the PLL cantilever driver 110 andthe deflection sensor 112 and other illustrated components are commonlyfound in atomic force microscopes and therefore further descriptions ofthe details thereof is not provided.

The IR-AFM system 100 further includes a signal generator 116, whichprovides an IR-F modulation signal to a photonic source 118, which inthis embodiment is a tunable laser. The IR-F modulation signal has afrequency above the range of interest for topographic following (e.g.,typically in the tens or hundreds of hertz (Hz)), but well below thefrequency of the mode being used for topographic imaging (or the lowermode frequency if multiple modes are being used for topographicimaging). As an example, the frequency of the IR-F modulation signal maybe in the range of 1 kilohertz (kHz) to 200 kilohertz (kHz). In someembodiments, the wavelength of the tunable laser 118 is controlled bythe computer 102 so that a range of wavelengths falls within theinfrared portion of the electromagnetic spectrum and can be swept toproduce a plot of IR-F vs. incident radiation wavelength. In someembodiments, the IR-F modulation signal applied to the tunable laser 118turns on and off the tunable laser so that the tunable laser is on atthe frequency of the IR-F modulation signal. The beam from the tunablelaser is directed to the probe tip/sample interface and IR-F in responseto the irradiation with the laser is detected by the probe tip106/cantilever 104.

In some embodiments, the IR-AFM system 100 further includes an FMdemodulator 120, a low pass filter 122, a topography servo 124, a zpiezo or a z-directional piezoelectric transducer 126, and a signalprocessing circuitry in the form of a lock-in detector or amplifier 128.The FM demodulator 120 receives a tracking signal from the PLLcantilever driver 110 and measures changes in the frequency of thecantilever 104, which includes changes due to IR-F. In an embodiment,the FM demodulator 120 generates a signal that changes with respect tovoltage when the vibration frequency signal of the cantilever 104deviates from a reference voltage. The output signal from the FMdemodulator 120 is transmitted through the low pass filter to allow onlylower frequency of the signal, which is used to maintain a desireddistance between the probe tip 106 and the sample of interest 114. Inparticular, the low-pass filtered signal is transmitted to thetopography servo 124, which controls the z piezo 126 to maintain thedesired distance between the probe tip 106 and the sample of interest114.

In some embodiments, the output signal of the FM demodulator 120 is alsotransmitted to the lock-in detector 128 to detect the IR-F signal usingthe IR-F modulation frequency signal from the signal generator 116 asthe lock-in reference frequency. The output of the lock-in detector 128corresponds to the amplitude of the component of the FM demodulatoroutput that is modulated at the IR-F modulation frequency. Since thelaser is modulated at the IR-F modulation frequency, and therefore theIR-F is modulated at this frequency, the resonant frequency of thecantilever will be frequency modulated at this frequency, and the FMdemodulator detector output will contain a component that is modulatedat this frequency. The output of the lock-in detector 128 therefore is asignal whose magnitude is proportional to the magnitude of the IR-Fgradient. The IR-F signal can be processed by the computer 102 togenerate an image of the sample of interest 114 or an IR-F signal acrossthe range of wavelengths generated by the laser.

Note that in the above discussion, only a single vibrational mode isdescribed to follow topography and generate an IR-F signal. It is alsopossible to use two separate modes, so that an IR-F amplitude signal canalso be derived. While the response time of this signal will be limitedby the cantilever quality factor Q, it may be useful to generate thissignal alongside that derived from the FM mode described above, allowingthe user to look at both signals depending on what type of measurementis desired.

In this two mode approach, the laser is modulated at two frequencies.The first frequency corresponds to related IR-AFM, which is usually thedifference frequency between the modes used for topographic sensing andIR-F sensing, but may also be the sum frequency of the two modes. Inaddition, a slower modulation, chosen as above for FM, is applied—forexample 1 kHz. With this arrangement, an amplitude IR-F signal isgenerated at the IR-AFM mode, and an FM IR-F signal is generated on bothmodes. Note, however, that since the AR-F mode is not driven (it onlyresponds to IR-F), it will have low or even zero amplitude at times,making it impossible to measure its frequency on an ongoing basis. Sincethe topographic mode is constantly driven, its frequency can be measuredat all times.

Note that the use of two modulation frequencies can be useful, even ifthere is no intention to derive an IR-F amplitude signal on its owncantilever mode. For example, assume that a laser is only capable ofshort pulses, but allows a pulse repetition rate up to 10 MHz. Thehighest effective duty cycle occurs when this pulsing is occurring atthe maximum frequency. Therefore, modulating at 10 MHz and 1 kHz wouldbe an effective way to generate an IR-F FM signal on the mode being usedfor topographic imaging. In effect, the rapidly pulsing laser is treatedas if it were a CW (continuous wave) source, modulated at the IR-Fmodulation frequency.

In accordance with an embodiment of the present disclosure, the IR-Fresponse of a thin film can be measured by an IR-AFM utilizing contactand non-contact modes. Contact modes include modes in which the probetip comes into contact with the upper surface of the thin film.Non-contact modes include modes in which the probe tip does not comeinto contact with the upper surface of the thin film. In an example of acontact mode, the force response of the thin film is detected bydeflection sensor 112 as a deflection of cantilever 104. In anotherexample of a contact mode, the probe tip is oscillated so that itperiodically contacts the upper surface of the film (e.g., by tappingthe upper surface of the film) and the force response of the film to theelectromagnetic energy exposure is detected as a change in the amplitudeor frequency of oscillation of the probe tip. In an example of anon-contact mode, the probe tip does not contact the film surface and isoscillated or vibrated. The force response of the film to theelectromagnetic energy exposure in this non-contact mode is detected asa change in the amplitude or frequency of the oscillation or vibrationof the probe tip. In another example of a non-contact mode, the probetip does not contact the film surface and is oscillated or vibrated atits resonant frequency. The force response of the film to theelectromagnetic energy exposure is detected as a change in the resonantfrequency of the probe tip/cantilever.

In accordance with an embodiment of the present disclosure, the forceresponse is determined during or immediately after exposure of the filmto electromagnetic radiation in the infrared portion of theelectromagnetic spectrum. The determined force response is used toevaluate a thickness of the analyzed film. This evaluation involvesidentifying a film thickness, correlated with the detected forceresponse, in a lookup table of force responses and thicknesses for amaterial making up the film. In accordance with an embodiment, thelookup table of force responses and thicknesses is generated for amaterial making up the film. In some embodiments, the lookup table ofresponses and thicknesses is generated for a material making up the filmof interest as well as one or more additional films, which are below thefilm of interest. Referring to FIG. 5, an example of a lookup table fora Material 1 is illustrated. The lookup table is specific for a Material1 making up the film for which the operator is evaluating thickness. Thelookup table includes a plurality of force responses A-1 correlated witha measured thickness 1-9 for a film of the material in question.Examples of materials for which lookup tables would be useful to includeconductive materials and non-conductive materials used in semiconductordevice fabrication. Examples of such conductive materials include,metals or metal compounds, including, but not limited to ruthenium,palladium, platinum, tungsten, cobalt, nickel, hafnium, zirconium,titanium, tantalum, aluminum aluminides and/or conductive metal carbides(e.g., hafnium carbide, zirconium carbide, titanium carbide, andaluminum carbide), and other suitable materials for N-type metalmaterials, such as Ta, TiAl, TiAlN, TaCN, other N-type work functionmetal, or a combination thereof, and suitable P-type work function metalmaterials include TiN, TaN, other P-type work function metal, orcombination thereof. Examples of non-conductive materials include a highdielectric constant (high-K) dielectric material such as hafnium oxide(HfO2), hafnium silicon oxide (HfSiO), hafnium silicon oxynitride(HfSiON), hafnium tantalum oxide (HMO), hafnium titanium oxide (HMO),hafnium zirconium oxide (HfZrO), low K dielectric materials such assilicon oxynitride (SiOxNy), Si₃N₄, SiO, SiO₂, SiONC, SiOC, and otherdielectrics or other suitable materials combinations thereof. Othermaterials for which lookup tables would be useful include germanium Geor silicon germanium SiGe, SiGeB, SiP, SiC or SiCP.

The force responses reflected in the lookup table are generated usingIR-AFM as described below in more detail. The measured thickness valuesin the lookup table are obtained by any known technique for determiningthicknesses of thin films on a substrate. One example of a technique fordetermining thicknesses of films on a substrate for purposes ofgenerating a lookup table in accordance with an embodiment describedherein includes utilizing transmission electron microscopy on across-section of a wafer substrate carrying the film of interest.Embodiments in accordance with the present disclosure are not limited toutilizing transmission electron microscopy on a cross-section of a wafersubstrate in order to determine thicknesses of films on a substrate thatwill be used to build a lookup table. Other metrology techniques thatprovide accurate measurement of the thicknesses of thin films on asemiconductor substrate can be used in accordance with some embodimentsof the present disclosure.

Referring to FIGS. 3A, 3B and 5, an embodiment of a method forevaluating thickness of a film on a substrate in accordance with thepresent disclosure is described. FIG. 3A, illustrates a wafer substrate310 and two films 312 and 314 on the wafer substrate 310. The wafersubstrate 310 and films 312 and 314 are similar to the wafer substrate10 and films 12 and 14 described above with respect to FIG. 1. Inaccordance with some embodiments of the present disclosure an IR-FMprobe schematically illustrated as atomic force microscopy tip 316supported at the end of cantilever 318. In accordance with thisembodiment, the size of the tip 316 is chosen based on whether a forceresponse of only the uppermost film 314 is desired or if the forceresponse of the uppermost film 314 and the underlying film 312 isdesired. If only a force response of the uppermost film 314 is desired,the size of the probe tip is selected such that the sensing depth isequal to or less than an estimated thickness of the uppermost film 314.If a force response of the uppermost film and the underlying film 312 isdesired, then the size of the probe tip is selected such that thesensing depth is greater than what is estimated to be the thickness ofthe uppermost film 314 or what is estimated to be the combined thicknessof the uppermost film 314 and the underlying film 312. Sensing depthsfor IR-FM probe tips range from about 1 nanometer to about 100nanometers, e.g., 40 nanometers or less. IR-FM probe tips useful inaccordance with some embodiments described herein are not limited tothese ranges of depths. For example, probe tips having greater or lessersensing depths can be used in accordance with embodiments of the presentdisclosure. As noted above, the IR-FM system schematically illustratedin FIG. 3A includes a source of electromagnetic radiation 320, e.g., asource of electromagnetic radiation having a wavelength within theinfrared portion of the electromagnetic spectrum. Evaluation of thethickness of film 314, in accordance with an embodiment of the presentdisclosure, includes irradiating over a range of wavelengths, the regionwhere the AFM tip 316 contacts or comes into close proximity of an uppersurface 322 of film 314. During this irradiation, the changes in forcesbetween the film 314 and the probe tip 316 are monitored and recorded asatomic force microscopy tip force (AFM Tip Force). These recorded forceresponses can be determined using AFM in a contact mode as describedabove or AFM in a noncontact mode as described above.

FIG. 3B illustrates an example of the results of a portion of an AFM tipforce measurement carried out on the sample with a layer 314 of Material1 and a layer 312 of Material 2 (illustrated in FIG. 3A). The plotdepicted in FIG. 3B is generated by exposing the surface of the sampleto a scan of infrared electromagnetic radiation while collecting AFM tipforce measurements. FIG. 3B illustrates a spike in the AFM tip force atapproximately 1000 nm wavelength and a less intense spike in the tipforce at approximately 2000 nm. The spike at approximately 1000nanometers represents the force response of film 314 and the spike atapproximately 2000 nm reflects a force response of the underlying layer312. In accordance with an embodiment of the present disclosure,thickness of layer 314 is evaluated by comparing the force responseillustrated in FIG. 3B with a lookup table such as that illustrated inFIG. 5. The lookup table in FIG. 5 includes force response values andmeasured thicknesses which have been independently derived for a layerof Material 1 on substrate 310, for example, by conducting TEM on across-section of a number of substrates each carrying a film of Material1 having a different thickness. The force responses in the lookup tablein FIG. 5 can be the peak force response at approximately 1000 nm or theforce responses in the lookup table can values associated with theintegrated area under the trace of the spike. Embodiments in accordancewith the present disclosure are not limited to these representations ofthe AFM tip force. Other characteristics of the AFM tip force vswavelength plots can be used to correlate with the measured forceresponses for the film being analyzed. In accordance with otherembodiments, the lookup table is generated by collecting force responsedata from a sample that includes a substrate that includes film layersof the same or similar composition as the substrate in question andmeasuring thicknesses of the upper film using TEM or similar technique.

In an alternative embodiment, a lookup table such as that illustrated inFIG. 6 is employed in accordance with embodiments of the presentdisclosure. The lookup table in FIG. 6 is similar to the lookup table inFIG. 5; however, the lookup table in FIG. 6 differs in that it isgenerated by carrying out IR-FM on a sample having a layer 312 ofMaterial 2 and a layer 314 of Material 1 and recording the forceresponse at two or more wavelengths (e.g., a wavelength where theMaterial 2 of layer 312 exhibits a spike in force response and theMaterial 1 of layer 314 exhibits a spike in force response) anddetermining thickness of at least layer 314 by conducting TEM on across-section of the substrate carrying the layer 314 of Material 1 andlayer 312 of Material 2. Embodiments described herein are not limited tousing lookup tables that include force responses at one or twowavelengths for a single layer or two layers. Embodiments describedherein include those that utilize lookup tables that include forceresponses at more than two wavelengths and that include measuredthickness values for more than one layer.

Referring to FIGS. 4A and 4B, another embodiment of a method forevaluating thickness of a film on a substrate in accordance with thepresent disclosure is described. FIG. 4B, illustrates a wafer substrate410 and two films 412 and 414. Wafer substrate 410 and films 412 and 414are similar to the wafer substrate 10 and films 12 and 14 describedabove with respect to FIG. 1 and the wafer substrate 310 and two films312 and 314 described above with respect to FIG. 3A. In accordance withthe embodiments of FIGS. 4A and 4B, the film 412 is similar in thicknessto the film 312 in FIG. 3A; however the film 414 is thinner than thefilm 314 in FIG. 3A. The probe tip 416, cantilever 418 and the source420 of electromagnetic radiation illustrated in FIG. 4A are identical tothe probe tip 316, cantilever 318 and the source 320 of electromagneticradiation described above with reference to FIG. 3A. The probe tip usedto generate FIG. 4B is identical to the probe tip used to generate FIG.3B and had the same sensing depth as the probe tip used to generate FIG.3B. In the interest of brevity, a description of the probe tip will notbe repeated here. As with the embodiment of FIG. 3A, in accordance withthis embodiment, the size of the tip 416 is chosen based on whether aforce response of only the uppermost film 414 is desired or if the forceresponse of the uppermost film 414 and the underlying film 412 isdesired. If only a force response of the uppermost film 414 is desired,the size of the probe tip is selected such that the sensing depth isequal to or less than what is estimated to the approximate thickness ofthe uppermost film 414. If a force response of the uppermost film andthe underlying film 412 is desired, then the size of the probe tip isselected such that the sensing depth is greater than what is estimatedto be the approximate thickness of the uppermost film 414 or what isestimated to be the combined thickness of the uppermost film 414 and theunderlying film 412. As noted above, the IR-FM system schematicallyillustrated in FIG. 4A includes a source of electromagnetic radiation320, e.g., a source of electromagnetic radiation having a wavelengthwithin the infrared portion of the electromagnetic spectrum. Evaluationof the thickness of film 414, in accordance with an embodiment of thepresent disclosure, includes irradiating over a range of wavelengths,the region where the AFM tip 416 contacts or comes into close proximityof an upper surface 422 of film 414. During this irradiation, thechanges in forces detected by the probe tip 416 are monitored andrecorded as atomic force microscopy tip force (AFM Tip Force). Theserecorded force responses can be determined using AFM in a contact modeas described above or AFM in a noncontact mode as described above.

FIG. 4B illustrates an example, of the results of a portion of an AFMtip force measurement carried out on the sample with a layer 414 ofMaterial 1 and a layer 412 of Material 2 illustrated in FIG. 4A. Theplot of FIG. 4B is generated by exposing the surface of the sample to ascan of infrared electromagnetic radiation while collecting AFM tipforce measurements. FIG. 4B illustrates a spike in the AFM tip force atapproximately 1000 nm wavelength and a spike in the tip force of aslightly greater peak value at approximately 2000 nm. The spike atapproximately 1000 nanometers represents the force response of film 414and the spike at approximately 2000 nm reflects a force response of theunderlying layer 412. In accordance with this embodiment as with theembodiment of FIGS. 3A and 3B, thickness of layer 414 is evaluated bycomparing the force response illustrated in FIG. 4B with a lookup tablesuch as that illustrated in FIG. 5 or with the look up table of FIG. 6.

As illustrated in FIG. 4B the peak of the spike in the AFM tip force isless at 1000 nanometers compared to the peak of the spike in the AFM tipforce at 1000 nanometers in FIG. 3B. This difference is attributable tofilm 414 in FIG. 4A being thinner than film 314 in FIG. 3A. Because film414 is thinner than film 314, the probe tip 416 is closer to underlyingfilm 412. The reduced thickness of film 414 and the resulting reductionin distance between probe tip 416 and film 412 compared to the distancebetween probe tip 316 and film 312 results in a less strong forceresponse at 1000 nm (force response of film 414) and a more strong forceresponse at 2000 nanometers (force response of film 412). In accordancewith another embodiment of the present disclosure, thickness of film 312in FIG. 3A and film 412 in FIG. 4A, can be evaluated utilizing the forceresponse of films 312 or 412 at 2000 nm by comparing the force responseat 2000 nm with a lookup table that includes independently determinedforce responses and thicknesses determined from a substrate including anupper film of the same material as the upper film of the sample beinganalyzed and an underlying film of the same material as the sample beinganalyzed.

In another embodiment, the thickness of layer 314 or layer 414 isevaluated utilizing the force response from the underlying layers 312 or412, respectively. In this embodiment, the thickness of layers 314 or414 is evaluated by comparing the force response of film 312 or 412 at2000 nm to a lookup table that includes independently derived forceresponses at 2000 nanometers correlated with independently derivedthickness values for films 314 or 414 determined from a substrateincluding an upper film of the same material as the upper film of thesample being analyzed and an underlying film of the same material as thesample being analyzed.

In accordance with another embodiment of the present disclosure, the AFMtip force scans illustrated in FIGS. 3B and 4B are utilized toqualitatively evaluate the relative thicknesses of films 312, 314, 412and 414. For example, a comparison of the AFM tip force scansillustrated in FIG. 3B and with the AFM tip force scan of FIG. 4B showthat at the 1000 nm wavelength the AFM tip force in FIG. 3B is greatercompared to the AFM tip force at the same wavelength in FIG. 4B. Thiswould indicate that film 314 from which FIG. 3B was generated is thickerthan film 414 from which FIG. 4B was generated.

In accordance with embodiments of the present disclosure, the thicknessof layers on a substrate can be evaluated with a horizontal resolutionon the order of less than 10 micrometers, less than 1 micrometer, lessthan 500 nanometers, less than 250 nanometers, less than 150 nanometers,less than 100 nanometers or less than 50 nanometers. For example, insome embodiments the horizontal resolution is about 100 nanometers. Thisbenefit of some embodiments of the present disclosure allows for theevaluation of thicknesses of layers that form part of nanometer sizedcritical features on a substrate.

In accordance with other embodiments of the present disclosure,thickness of a film on the substrate is evaluated using an alternativeto IR-AFM, such as scanning capacitance microscopy (SCM). SCM is avariety of scanning probe microscopy in which a narrow probe electrodeis positioned in contact with or close proximity of a sample's surfaceand scanned. SCM characterizes the surface of the sample usinginformation obtained from a change in electrostatic capacitance betweenthe surface and the probe. When scanning capacitance microscopy is usedin accordance with an embodiment of the present disclosure, capacitanceof a film is determined using scanning capacitance microscopy equipment.The determined capacitance of the surface film is compared to a lookuptable that includes independently determined capacitance values andindependently measured thicknesses of surface films of the same materialas the material making up the film being analyzed. The independentlymeasured thickness of surface films of the same material as the materialmaking up the film being analyzed are derived using TEM oncross-sections of substrates that include films of the same material asthe sample being analyzed.

Referring to FIG. 7, a method 700 for evaluating thickness of a film ona substrate in accordance with an embodiment of the present disclosureis illustrated. The method includes step 702 of exposing a film toelectromagnetic radiation in the infrared portion of the electromagneticspectrum. During the exposure of the film to electromagnetic radiationin the infrared portion of the electromagnetic spectrum, at step 704, aforce response of the irradiated film is detected using IR-FM asdescribed above. At step 706, the detected force response is then used,to evaluate thickness of the film being analyzed. Evaluation of thethickness of the film being analyzed includes comparing the detectedforce response to a lookup table that includes independently measuredforce responses for a plurality of films of the same material as thefilm being analyzed and independently determined thicknesses of theplurality of films.

FIG. 8 illustrates another method 800 for evaluating thickness of asurface film on a substrate in accordance with an embodiment of thepresent disclosure. In the method of FIG. 8, a substrate including aplurality of films is exposed at step 802 to electromagnetic radiationfrom the infrared portion of the electromagnetic spectrum. During theirradiation step 802, a force measurement in a non-contact mode isperformed at step 804 using IR-FM. At step 806, a force response isdetected at a first wavelength of the infrared spectrum. At step 808, aforce response is detected at a second wavelength of the infraredspectrum. The force response detected at a first wavelength of theinfrared spectrum and the force response detected at a second wavelengthof the infrared spectrum is used to evaluate the thickness of thesurface film at step 810. Evaluation of the thickness of the surfacefilm being analyzed at step 810 includes comparing the detected forceresponses at the different wavelengths to a lookup table that includesindependently measured force responses at the two different wavelengthsfor a plurality of films of the same material as the films beinganalyzed and independently determined thicknesses of the plurality offilms.

Referring to FIG. 9, another method 900 for evaluating a film on asubstrate in accordance with the present disclosure includes a step ofexposing a plurality of films to electromagnetic radiation from theinfrared portion of the electromagnetic spectrum at step 902. During theirradiation of the plurality of films, at step 904, and atomic forcemicroscopy force measurement is carried out on the films. At step 906, aforce response of the first film at a first wavelength is detected. Thisfirst film can be an upper surface film but is not limited to an uppersurface film. At step 908 a force response of a second film at a secondwavelength is detected. In some embodiments, the second film is anunderlying film below the upper surface film. At step 910, the detectedforce response of the second film at the second wavelength is used, toevaluate thickness of the first film. The thickness of the first film isevaluated by comparing the force response of the film in question to alookup table that includes independently derived force responses at thewavelength in question correlated with independently derived thicknessvalues of films determined from a substrate including an upper film ofthe same material as the upper film of the sample being analyzed and anunderlying film of the same material as the sample being analyzed.

In one embodiment of the present disclosure, a thickness of a thin filmon a substrate is evaluated. In this embodiment, the film is exposed tononvisible electromagnetic radiation, e.g., electromagnetic radiation inthe infrared portion of the electromagnetic spectrum. The exposed filmis subjected to an atomic force microscopy technique to detect a forceresponse of the film to the electromagnetic radiation. The detectedforce response is used, to determine a thickness of the film.

In another embodiment of the present disclosure, the thickness of a filmon a substrate is exposed to infrared electromagnetic radiation. Whileexposing the film to the infrared electromagnetic radiation, an atomicforce microscopy technique is applied to the film to detect a forceresponse of the film to the electromagnetic radiation. A thickness ofthe film is then determined using the results of the atomic forcemicroscopy technique.

In another embodiment, a plurality of films on a substrate is exposed toelectromagnetic radiation in the infrared portion of the electromagneticspectrum. During this irradiation, a non-contact atomic force microscopytechnique is applied to the films on the substrate to detect a forceresponse of the film at a first wavelength of the radiation and at a 2′wavelength of the radiation. These detected force responses are used, toevaluate a thickness of one of the plurality of films.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method for evaluating thickness of a film on a substrate,comprising: exposing the film to non-visible electromagnetic radiation;detecting a capacitance response of the film to the exposing the film tothe non-visible electromagnetic radiation; and using the capacitanceresponse of the film from the detecting step to determine a thickness ofthe film.
 2. The method of claim 1, wherein the exposing the film tonon-visible electromagnetic radiation includes exposing the film toelectromagnetic radiation in a near infrared portion of theelectromagnetic spectrum.
 3. The method of claim 1, wherein thedetecting a capacitance response of the film includes determining acapacitance response of the film using scanning capacitance microscopy.4. The method of claim 3, wherein the scanning capacitance microscopy isconducted in a non-contact mode.
 5. The method of claim 3, wherein thescanning capacitance microscopy is conducted in a contact mode.
 6. Themethod of claim 5, further comprising: exposing a first underlying film,below the film, to the non-visible electromagnetic radiation; anddetecting a capacitance response of the first underlying film to theexposing the first underlying film to the non-visible electromagneticradiation; and using the capacitance response of the first underlyingfilm from the detecting step for the first underlying film incombination with the capacitance response of the film from the detectingstep for the film to determine a thickness of the film.
 7. The method ofclaim 6, further comprising: exposing a second underlying film, belowthe film and the first underlying film, to the non-visibleelectromagnetic radiation; and detecting a capacitance response of thesecond underlying film to the exposing an underlying film and firstunderlying film to the non-visible electromagnetic radiation; and usingthe capacitance response of the second underlying film from thedetecting step for the underlying film in combination with thecapacitance response of the film from the detecting step for the film todetermine a thickness of the film.
 8. The method of claim 6, wherein thecapacitance response of the film occurs at a first wavelength ofelectromagnetic radiation and the capacitance response of the underlyingfilm occurs at a second wavelength of electromagnetic radiationdifferent from the first wavelength.
 9. The method of claim 1, whereinthe using the capacitance response of the film from the detecting stepto determine a thickness of the film includes identifying a thicknesscorrelated with a capacitance response in a look up table of capacitanceforce responses and film thicknesses for a material making up the film.10. A method for determining thickness of a film on a substrate,comprising: exposing the film to infrared electromagnetic radiation;while exposing the film to the infrared electromagnetic radiation,performing a capacitance measurement on the film using scanningcapacitance microscopy; determining a thickness of the film using theresults of the capacitance measurement on the film.
 11. The method ofclaim 10, wherein the capacitance measurement using scanning capacitancemicroscopy utilizes changes in electrostatic capacitance between asurface of the film and a capacitance probe used in the scanningcapacitance microscopy.
 12. The method of claim 10, wherein the film isthe uppermost film.
 13. The method of claim 10, wherein the capacitancemeasurement is carried out in a contact mode, wherein a probe of ascanning capacitance microscopy equipment contacts a surface of thefilm.
 14. The method of claim 10, wherein the infrared electromagneticradiation is near infrared electromagnetic radiation.
 15. The method ofclaim 10, where the capacitance measurement is carried out in anon-contact mode, wherein a probe of a scanning capacitance microscopyequipment does not contact the surface of the film.
 16. A method forevaluating thickness of a film on a substrate, comprising: exposing aplurality of films on the substrate to electromagnetic radiation in theinfrared portion of the electromagnetic spectrum; while exposing theplurality of films to the electromagnetic radiation in the infraredportion of the electromagnetic spectrum, performing a scanningcapacitance microscopy measurement on the plurality of films using ascanning capacitance probe microscope operating in a non-contact mode;detecting a scanning capacitance probe microscopy response of theplurality of films at a first wavelength of the electromagneticradiation in the infrared portion of the electromagnetic spectrum;detecting a scanning capacitance probe microscopy response of theplurality of films at a second wavelength of the electromagneticradiation in the infrared portion of the electromagnetic spectrum; usingthe detected scanning capacitance probe microscopy response at the firstwavelength and the detected scanning capacitance probe microscopyresponse at the second wavelength to evaluate a thickness of one of theplurality of films.
 17. The method of claim 16, wherein the using thedetected scanning capacitance probe microscopy response at the firstwavelength and the detected scanning capacitance probe microscopyresponse at the second wavelength to determine a thickness of one of theplurality of films includes identifying a thickness correlated with acombination of the scanning capacitance probe microscopy response at thefirst wavelength and a scanning capacitance probe microscopy response atthe second wavelength in a look up table of scanning capacitance probemicroscopy responses at the first wavelength and scanning capacitanceprobe microscopy responses at the second wavelength for a materialmaking up the one of the plurality of films.
 18. The method of claim 16,wherein the plurality of films have a combined thickness of less than 40nanometers.
 19. The method of claim 16, wherein the one of the pluralityof films is the uppermost film.
 20. The method of claim 16, wherein theone of the plurality of films is not an uppermost film.